1. Field of the Invention
The present invention relates to a vehicle brake system, and more particularly, to a disc brake for large road vehicles, such as tractors and trailers, using existing pneumatic or air systems.
2. Description of the Prior Art
Canadian Patents 1,112,189, issued Nov. 10, 1981 and 1,140,486, issued Feb. 1, 1983, and U.S. Pat. No. 4,102,438, issued Jul. 25, 1978, Yvon Rancourt, which are incorporated herein by reference, describe a disc brake for heavy road vehicles wherein the brake shoes are in contact with the much larger disc area, and a suitable brake cooling system is provided to cool the disc, thus making disc brakes practical for such vehicles. The present invention is an improvement over the above-mentioned patent.
There are braking systems available on various types of vehicles which include a positive mechanical brake of the type known as a fail-safe brake, that is, where the brakes are applied when pressure is released from the brakes. U.S. Pat. No. 3,547,234, Cummins, Dec. 15, 1970, describes a service brake for earthmoving trucks or tractors which includes a hydraulic brake system using a plurality of discs, and these discs are mechanically preloaded by a spring to provide a fail-safe brake. U.S. Pat. No. 4,057,297, Nov. 8, 1977, Beck et al, includes a brake system which has been preloaded by means of a spring, including the discs of the type described n the Cummins Patent. This pressurized air operated system uses a series of valves to modify the pressure exerted on the torque converter in order to avoid damage to the differential. This is a system that is utilized in very heavy machinery such as tractors, etc. These patents represent the state of the art in terms of fail-safe type brake systems using preloaded mechanical devices such as springs. The structures are complicated by the need to be adapted on heavy vehicles. What is required is a fail-safe type brake system of simple construction using pneumatic pressure for releasing the brakes and utilizing a simple disc brake construction of the type described in the Rancourt Patent wherein the disc is mounted to the adapter sleeve of a wheel on the vehicle and the brake housing is mounted to the vehicle on a dead axle.